It should also be noted that the virtual times of any event A and B should follow the above rules only if there are events which directly or indirectly have causality amongst A and B. The virtual time of each event in a process must be less than the virtual time of the next event at that process. The virtual send time of each message must be less than its virtual receive time. Some fundamental rules which must be observed for virtual time: The main purpose is to have a single virtual time (which may also be in sync with the real time) across the system so that processes can always operate in an opaque manner when in actuality, it is an unpredictable entity.Īll processes communicate with each other (either locally or remotely) via messages which mainly consist of 4 primary fields: sender, virtual send time, receiver, virtual receive time. Virtual time itself is a global, one-dimensional, temporal coordinate system imposed on a distributed computation it is used to measure computational progress and to define synchronization. This post will cover the lookahead-rollback used by the Time Warp algorithm since, though not intuitive, it is leads to elegant and efficient solutions when the cons are compared for each of the techniques.Ī virtual time system is a distributed system executing in coordination with an imaginary virtual clock that ticks virtual time. Some common forms of synchronization techniques in distributed systems are block-resume, abortion-retry, lookahead-rollback. One of the most important and difficult things to manage in distributed systems is managing synchronicity using time. What is virtual time and why do we need it?Īs distributed systems have progressed and been adopted over the last decade, there have been numerous technologies in different segments like databases, caches, message queues, etc which are built on top of other frameworks which abstract away the difficulty of managing distributed systems.
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